The invention relates to a method for operating a catalytic converter of an internal combustion engine, especially of a motor vehicle, wherein the catalytic converter is loaded with nitrous oxides and unloaded and wherein the NOx emissions downstream of the catalytic converter are measured. Likewise, the invention relates to a control apparatus for an internal combustion engine, especially of a motor vehicle, as well as an internal combustion engine especially for a motor vehicle.
A method of this kind, a control apparatus of this kind and an internal combustion engine of this kind are, for example, known for a so-called gasoline direct injection. There, the fuel is injected into the combustion chamber of the internal combustion engine in a homogeneous operation during the induction phase or in a stratified operation during the compression phase. The homogeneous operation is preferably provided for the full-load operation of the engine; whereas, the stratified operation is suitable for idle operation and part-load operation. In a direct-injecting internal combustion engine of the above kind, a switchover takes place between the above-mentioned operating modes, for example, in dependence upon the requested torque.
Especially for carrying out the stratified operation, it is required that a storage catalytic converter be present with which developing nitrogen oxides can be intermediately stored in order to reduce the same during a subsequent homogeneous operation. This storage catalytic converter is loaded in the stratified operation with nitrogen oxides and is again unloaded in the homogeneous operation. An NOx sensor is mounted downstream of the catalytic converter for controlling and monitoring. The NOx sensor is provided for measuring NOx emissions of the discharging exhaust gas.
Parts of the catalytic converter can become defective because of the deterioration thereof or for other reasons.
It is an object of the invention to provide a method for operating a catalytic converter of an internal combustion engine with which a defect of the catalytic converter can be detected.
This object is solved in accordance with the invention with a method of the kind mentioned initially herein in that the catalytic converter is only partially loaded, that an increased NOx emission is generated in advance or in the catalytic converter and that a conclusion is drawn as to the operability of the catalytic converter from the NOx emissions measured downstream. The object is correspondingly solved with a control apparatus and an internal combustion engine of the respective types mentioned initially herein.
The catalytic converter can reduce the increased NOx emissions generated ahead of or therein via the only partial loading of the catalytic converter. In this way, a lower NOx emission is present at the output of the catalytic converter than the initially generated NOx emission. From this reduction, a conclusion is drawn in accordance with the invention as to the operability of the catalytic converter. If a significant reduction of the initially increased NOx emission is present, then a conclusion can be drawn at least insofar as to a proper operation of the catalytic converter.
The catalytic converter is, however, recognized as being defective when an increased NOx emission is measured. In this case, the initially increased NOx emission was not reduced by the catalytic converter. This defines an operation of the catalytic converter which is not proper.
In an advantageous embodiment of the invention, the increased NOx emission is generated ahead of or in the catalytic converter by a discharge thereof. An increased NOx emission arises from the switchover to the discharge. Since the catalytic converter is not fully loaded, this increased NOx emission arises at the beginning or at least in the interior of the catalytic converter. In this way, for an intact catalytic converter, the increased NOx emission can be reduced again within the catalytic converter itself. There is then no NOx emission or only a very slight NOx emission measured by the NOx sensor at the output of the catalytic converter from which a conclusion can be drawn as to a proper operation of the catalytic converter.
Likewise, it is advantageous, when the increased NOx emission is generated ahead of or in the catalytic converter by: a reduction of the exhaust-gas recirculation rate and/or by an early shift of the ignition time point and/or by a reduction of the fuel pressure. Alternatively or additively, the increased NOx emission can be generated by chemical NOx sources wherein, for example, urea or nitrate is introduced ahead of the catalytic converter. Furthermore, the increased NOx emission can be generated by a spark plug mounted forward of the catalytic converter.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an internal combustion engine, especially of a motor vehicle. A program is stored on the control element which can be run on a computing apparatus, especially on a microprocessor, and is suitable for executing the method in accordance with the invention. In this case, the invention is therefore realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method for whose execution the program is suitable. As a control element, an electric storage medium is especially applicable, for example, a read-only-memory or a flash memory.
Further features, possibilities of application and advantages of the invention will become apparent from the description of the embodiments of the invention which follow and which are shown in the figures of the drawing. All described or illustrated features form the subject matter of the invention individually or in any combination independently of the composition thereof in the patent claims or their dependency as well as independently of their formulation in the description or their illustration in the drawing.